1. Field of the Invention
The present invention relates to the technical sector of electronic methods and systems for controlling an electric apparatus.
In particular, the invention relates to methods for estimating the operating current and the state of charge of a battery or a battery pack for a vehicle or, likewise, of a battery cell (simply defined in this description as “cell”), without direct detection of current under operating conditions.
Furthermore, the invention relates to a control device of a battery pack or cell, which performs the aforesaid method, and a battery pack or cell for a vehicle capable of monitoring the operating current and the state of charge, by virtue of the aforesaid method, without need to be equipped with current sensors.
2. Description of the Related Art
Knowing the voltage and electric current of a battery, of a battery pack or cell composed of electrochemical cells (in particular, in the “automotive” field, in the context of motion systems and batteries for electric or hybrid drive vehicles) is a very important information for the correct management and control of the battery, battery pack or cell.
The acquisition of voltage, current and temperature of the cells of a battery pack or cell is required for knowing the state of charge of the cell itself, and for the correct management and protection thereof, so as to avoid the triggering of secondary physical-chemical processes which would lead to the degradation of performance and durability of the cell, and even, in extreme cases, to the phenomenon known as “thermal runaway”, with serious consequences, up to the blaze or explosion of the battery pack or cell.
Furthermore, knowing the current, which may be common to several modules or to the whole battery pack or cell, is useful for determining the state of charge (SOC) of the cell.
In common background art solutions, knowing the battery or cell current is obtained by the direct detection of such current, typically using physical current sensors of the shunt type or Hall-effect-based sensors, installed on the battery pack or cell itself.
In the case of shunt type sensors, the current is determined by measuring the voltage on a resistor with a known value on which the battery or cell current is circulated.
In the case of Hall-effect-based sensors, the current is determined by measuring the Hall voltage generated on a conductor crossed by the current of the battery or cell and subjected to an electromagnetic field.
Both of the aforementioned cases envisage the need to provide a battery pack or cell equipped with a plurality of current sensors, which entails the disadvantage of increasing the complexity and cost of the battery pack itself or of the cell.
The need therefore arises to identify methods for estimating the current of the battery or cell (i.e., the “battery or cell current”), regardless of the direct acquisition of such current using current sensors.
This approach, however, encounters the further technical problem of obtaining a current estimate sufficiently accurate to be actually usable. In fact, the required accuracy provides for minimizing the error of the estimate within limited percentages (for example, comparable to or less than 5%).
A battery or cell current estimate of such accuracy is not at all easy to obtain, since the actual battery or cell current, at a given moment, not only depends on the battery or cell operating voltage detected at that instant, but also depends, in a complex manner, on the temperature and the state of charge of the battery or cell (hence on the history and life-time thereof). Therefore, there are no simple analytical formulas which, by knowing the battery or cell voltage and temperature, allow to obtain the battery or cell current, with the accuracy required.
Furthermore, since the relationship between the battery or cell current and the other electrical and thermal quantities of the battery or cell also depends on degradation and aging, the need is further felt to have an estimation method which suitably takes into account such aspects.
The known solutions, in this regard, do not satisfy the requirements mentioned above.
In light of the foregoing, mainly in the field of automotive applications, and in particular in the context of battery packs for electric or hybrid vehicles, the need is felt for methods for estimating the current and the state of charge of the battery or cell, providing a sufficiently accurate information regarding the current and regarding the state of charge of the battery or cell, while avoiding the need for a direct acquisition of the battery or cell current under operating conditions.